Understand the guiding principles of ¿clean code¿ and how it applies to modern front-end development, accessibility (a11y), semantics, performance, and the Green Web. Highlighting key topics ranging from the foundations of JavaScript and HTML to popular frameworks like React, this book provides best practices to ensure code and applications are easier, more efficient and cost effective to run. Using a web-based application as an example, yoüll begin by cleaning and improving its code base by dividing the JavaScript into smaller, reusable and composable functions without side effects. Then, yoüll improve the HTML code base by applying "Disability Driven Design" patterns, focusing on semantics before moving on to improving the architecture with a functional style (immutable, modular and composable). Because the web today needs to be green with reduced loading time and energy consumption, yoüll apply some tips and tricks to improve code performance and see how to best monitor it in a continuous and scalable way. What Yoüll Learn See how the JavaScript engine works and memory management. Explore in greater detail key focus areas of accessibility and green computing Make applications easier and more cost-effective to run Look closely at clean and sustainable development using JavaScript and React Who This Book Is For Programmers, developers, engineers and product managers who are looking at cost-efficient ways to make their applications run more smoothly and efficiently.